The administration of medical liquids is largely carried out by gravity-induced hydrostatic pressure infusion of the liquid from a bottle or other container suspended above the recipient an acceptable distance. The liquid empties by gravity at a rate of flow which can be regulated by what is known as a drop-by-drop device which reduces the rate of flow by restriction or compression of the flexible tube carrying the liquid which is to be injected. Although this equipment is used in hospitals, it is however bulky, difficult to move, clumsy and slow to set up. Further, the flow rate is not easily controlled since variations in relative positions of the receiving portion of the patient and the dispensing bottle may occur with time as the patient or bottle may be shifted about.
Moreover, previously available pressure-assisted administration devices are often quite complicated and expensive, and also often lack portability. Further, these known apparatuses are often unable to provide, as well as continuously maintain for a long time, a desired flow rate.
Still further, most known administration devices require that the drug solution is discharged from its original container, i.e. from the prepackaged, disposable, standard medical containers, and into a administration reservoir of the administration apparatus. This is normally a rather tedious and cumbersome task, and also invokes a risk for contamination, since the solution must pass through additional handling steps in the preparation and transfer process, prior to being introduced to a patient.
In many situations, a patient may also require a very slow and continuous introduction of medicament liquid into the patient's system, such as a few milliliters per hour for several hours, or sometimes even a day or more. It is therefore very important that these medicament liquid or pharmaceutical solution doses be administered with a highly accurate introduction rate (flow rate), which is maintained very stable during the entire process.
To this end, many of today's administration apparatuses comprises complex electronic systems. For example, such systems may include complex valve arrangement by which the fluid is introduced into the chamber and withdrawn there from, and controlled by a electronic circuitry which includes pressure sensors and logic circuitry which controls fluid pumps which move the liquid. While relatively compact and accurate, these systems are also highly complex, expensive and requires a great deal of electrical power to operate. Further, these apparatuses are solely intended for multi-time use, which necessitates cumbersome and tedious cleaning and sterilization of the apparatuses before re-use, and also invokes a risk for contamination of the patient.
Further, it is known from the prior art to produce portable and mechanical administration devices. For example, U.S. Pat. No. 3,460,277 discloses a self-contained portable administration apparatus using CO2 cartridges to obtain a relatively precisely regulated gas flow to displace a medical arranged in a pressure collapsible container. To this end, the pump device comprises a casing comprising a collapsible bladder holding the fluid to be driven (the medical liquid) and a second inflatable bladder to be filled with a driving fluid, whereby expansion of the second bladder causes the medical liquid to be controllably expelled. However, this device is still relatively complicated and expensive to produce, and there is also a problem of obtaining a sufficiently continuously stable and controllable pressure acting of the pressure collapsible container holding the medical liquid. Similar problems are also encountered in the apparatus disclosed in U.S. Pat. No. 5,954,696 and U.S. Pat. No. 4,673,392, which are both related to similar types of administration apparatuses.
Consequently, there is still a need for administration apparatuses which are both capable of providing a sufficiently stable and controllable flow rate, and at the same time are safe and inexpensive to produce and use.